High-speed high-pressure vacuum pump



WM. J. H. cox ET AL v432,22

HIGH-SPEED HIGH-PRESSURE VACUUM PUMP Filed April 30, 1945 WITNESSES.INVENTORS Jose h H. Cox, Dwi ht LHoppw' W MVQIJML JLJ fluyugt P [0az'aco.

Patented Dec. 9, 1947 HIGH- SPEED HIGH-PRESSURE VACUUM PUMP Joseph H.Pittsburgh, Dwight L. Hopper,

Wilkinsburg, and August P. Colaiaco, Pittsburgh, Pa., assignors toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application April 30, 1945, Serial No. 591,080

3 Claims. 1

Our invention relates to a high-speed, highpressure oil diffusion vacuumpump, and particularly to an oil diffusion pump capable of operating athigh speeds against a high back pressure. a

In the utilization of vacuum systems, it is frequently desirable torapidly evacuate relatively large capacities. The vacuum system fordoing this comprises a high vacuum pump, such as an oil diffusion pumpand a secondary or backing pump usually of'the oil sealed rotaryvariety.

As heretofore constructed, the oil diffusion pumps have been able tohandle large quantities of gas only when pumping at a very low backpressure ofthe order of 150 microns. However, to effectively handlelarge volumes of air, the oil sealed mechanical pump should have arelatively large fore pressure, such as the order of 500 to 1000microns.

Referring to our invention, we have provided an oil diffusion pump whichwill deliver large quantities of gas at a back pressure of the order of500 to 1000 microns and still produce the desired high vacuum, thusmeeting the needs of the backing pump and producing a high speed pumpingcombination.

In order to produce this type of pump, we have provided a boiler havinga large oil vapor evolving surface and provided the boiler with enlargedheat conducting surfaces so that large quantities of heat may beconducted into the boiler at low temperature levels and without causinglocal hot spots violent boiling or turbulence in the boiler.

The vapor evolved from the boiler is maintained in a high head pressurechamber and is conducted to a chimney connected to a substantiallyaxially directed pumping jet which acts not only to entrain gases by thejet action, but also is enclosed in a cooled condensing chamber to actin a normal manner of a condensing pump. In order to prevent reversevapor flow in the jet chamber, a vapor chimney is secured in gas tightrelation, preferably by means of a suitable packing between the bottomof the chimney and the top of the pressure chamber.

The condensing chamber is connected to a cooled return conductorextending below the oil surface in the boiler, so that the oil acts as aseal to prevent vapor returning to the jet chamber through the oilreturned.

It is accordingly an object of our invention to provide an oil diffusionpump operable against a high back pressure.

It is a further object of our invention to provide an oil diffusion pumphaving high-speed,

high-pressure characteristics.

It is a further object of our invention to provide an oil diffusionboiler having low heat levels with high heat transfer.

It is a further object of our invention t provide an oil diffusion pumpwhich eliminates back streaming in a pumping chamber.

Other objects and advantages of our invention will be apparent from thefollowing detailed description taken in conjunction with theaccompanying drawing, in which the figure is a sectional elevation of apump according to our invention.

In the exemplary embodiment of our invention, the high-pressure,high-speed pump comprises an oil boiler I0 having a relatively largevapor evolving surface I I to produce large volumes of oil vapor at highhead and to which is connected a pressure chamber I2 preferably ofconsiderably less diameter than the diameter of the boiler I0, and ofsufiicient height to support a column of oil l3 equal to the headproduced by the boiler,

In order to prevent destructive distillation of r the oil in the boilerIll, an external heater I4 is applied to a portion I5 of the boiler walland a plurality of bafiies l6 which may be of any desired configurationare connected to the heated portion I5 of the container and extend intothe oil to provide a. large heat transferring surface, so that largequantities of heat may be transferred a relatively low levels oftemperature and without causing excessive boiling or turbulence of theoil.

The external portions of the boiler l0 and the pressure chamber I2 arecovered with heat insulating lagging II to prevent excessive losses ofheat from the boiler surfaces.

A vapor chimney 20 is connected to the pressure chamber I2 and in orderto prevent back streaming or leakage around the chimney 20, a packing 2|is provided, preferably in a groove 22 at the bottom of the chimney 20,and means such as a bolt 23 is provided for drawing the chimney 20 intogas tight relation with the packing material 2 I.

The chimney 20 terminates in a pumping jet 30 herein illustrated as ofthe axially directed variety which by jet action helps to entrain gasmolecules entering through the connection 29.

The jet 30 is enclosed in a condensing chamber 3|, the walls. 32 ofwhich are cooled by suitable means such as cooling coils 33 appliedpreferably to the external surface thereof.

In order to prevent revaporization of oil flowing about the base of thechimney 20 the cooling 3 coils 83 are extended adjacent to the groove22, and the plate containing groove 22 as well as the unprotected partof the pressure column is protected by a baflle 25 secured in spacedrelation to the inner side of the pressure column and extending adjacentthe groove. An oil return 34 is provided and so connected to thecondensing chamber 3! that any oil collecting in the chamber 3!immediately flows into the oil return 34 and does not provide stagnantpools which might absorb heat and thereby revaporize. The oil return 34is external to the pressure chamber l2 to'prevent leakage of heat intothe returning oil and extends to a point adjacent the bottom of theboiler In so that the oil l3 in the return connection 34 provides avapor seal between the boiler l and the condensing chamber 31 and thusprevents back streaming through the 011 return 34.

In the operation of our pump heat is applied to the boiler to producevapor at a high head and delivered through the axially directed jet 30to draw gas through the intake 29 and deliver the same through theoutlet 35 to a mechanical pump (not shown). Because of the pressure anddirection of the vapor in the jet the pump will deliver gas against aback pressure of the order of 1000 microns even when the pressure of,the inlet approaches a pressure of zero.

The ability to operate against a high back pressure enables themechanical pump to operate with a high fore pressure thus producing ahigh speed evacuation of any chamber connected to inlet 29.

While for purpose of description we have shown and described a specificembodiment of our invention, it will be apparent that changes andmodifications can be made therein without departing from the true spiritof our invention and by the scope of the appended claims.

We claim as our invention:

1. A- vacuum pump comprising a boiler of large surface area, an externalheater applied to said boiler, bailies in said boiler and in contactwith the heated exterior surface to increase the heat conducting area, apressure chamber of less diameter than said boiler, a vapor chimneyconnected to said pressure chamber, a vapor jet supplied by saidchimney, a condensing chamber about said jet and a condensate returnfrom said condensing chamber to a point below the surface of the liquidin the boiler, said return being so connected that all condensaterapidly drains from the condensating chamber, a vapor seal between saidboiler and said chimney and means for cooling said vapor seal.

2. A high pressure vacuum pump comprising a boiler chamber, a heatertherefor, means for distributing the heat uniformly throughout saidboiler, a vapor chamber connected to said-boiler,

, a vapor jet fed from said boiler, and cooling means to prevent backstreaming of vapor about said let.

3. An oil diiTusion vacuum pump comprising a boiler having a large vaporevolving area, heating means for said boiler, means for preventing localexcess temperature in said boiler, a vapor jet fed by said boiler, acondensing chamber about said jet, a condensate return from said chamberto a point adjacent the bottom of said boiler, and cooling means forpreventing revaporization of condensate in said condensing chamber.

JOSEPH H. COX. DWIGHT L. HOPPER. AUGUST P. COLAIACO.

REFERENCES CITED The following references are of record in the

